Renal ischemia in vivo and ATP depletion in vitro cause renal epithelial cells to die by apoptosis. Apoptosis is caused by mitochondrial membrane injury that is regulated by well-characterized members of the BCL2 protein family. We have established that ATP depletion in renal cells increases bax (pro-apoptotic), decreases bcl2 (anti-apoptotic) and causes apoptosis. Concomitant with this pro-apoptotic change in the bcl2:bax ratio, cytochrome c and apoptosis inducing factor (AIF) translocate from mitochondria into the cytosol and state III mitochondrial respiration is reduced. Cytosolic cytochrome c activates caspases, whereas AIF enters the nucleus, activates endonucleases and causes DNA degradation. Prior heat stress, sufficient to induce hsp72, a molecular chaperone, stabilizes the bcl2:bax ratio, decreases cytochrome c and AIF leak, reduces caspase activation and DNA degradation, completely preserves organeile function and enhances long term survival after ATP depletion. The selective over-expression of hsp72 mimics the protective effects of prior heat stress on apoptosis and renal cell survival. The fact that hsp72 binds bcl2 (but not bax), cytochrome c and AIF suggests that hsp72 itself is an anti-apoptotic protein. We hypothesize that hsp72 decreases primary injury to the mitochondrial membrane caused by bax and inhibits the secondary, pro-apoptotic effects of leaked cytochrome c and AIF on caspase activation and DNA degradation, respectively. In isolated organelles and intact ceils, this study will: (1) determine whether cytoprotection by hsp72 against bax-mediated mitochondrial membrane injury requires bcl2; (2) evaluate the ability of hsp72 to rescue bcl2 function, prevent caspase activation and/or to inhibit AIF-mediated DNA degradation and (3) identify the specific hsp72 domain(s) responsible for its anti-apoptotic actions. To achieve these AIMS, hsp72, bax and bcl2 content will be manipulated in renal epithelial cells using adenoviral infection with established vectors including wild type human hsp72, antisense and known hsp72 deletion mutants with specific functional defects. These studies will identify the anti-apoptotic mechanism(s) of hsp72. These insights can prompt the development of preemptive strategies for preventing renal cell injury during ischemic insults as well as other forms of renal injury in which apoptosis contributes to organ failure.